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>>Can I ask a different question about the Thermastor product?
>>How do you make it work in conjunction with the main system
>>that has dehumidification mode built in? Thanks

Let an amateur try his hand at the answer. I believe you are speaking of the Thermastor model which is not free-standing but connected to the central AC ductwork. This question could equally apply to any of the other brands of central dehumidification.

I believe it will pretty much operate independently of the central AC dehumidification function, neither will interfere with the other but each will lessen the work the other is asked to do. Probably with typical settings the dehumidifier will do most of the work and the central AC will seldom be called for reasons other than temperature control. Of course during mild humid weather, you will get good humidity reduction with this equipment, something you cannot do without overcooling if you rely on the AC alone.

The downside of course is you have to pay for a pretty fancy dehumidifier in addition to your central AC. But you already know that<g>.

If any of the real board experts can add to what I said, or correct me, that will simply make things more interesting.

Seperate stats

>>I'd think that you would want separate humidity and temperature stats to control such a system.
>>Humidistat to control the dehumidifier, thermostat to control the AC.

I totally agree, in fact have trouble imagining any other way to set it up. I just assumed 1) the dehumidifier had a humidistat somewhere, and 2) the AC was set up with both a thermostat for cooling, and a humidistat for humidity removal running (when cooling was not called).

This thread is a few months old, but of interest to me as I am considering an Ultra Aire system to supplement the new 18 SEER Lennox heat pump we installed. Long story short, after unit was installed, ducts in attic sweated profusely. Without all the gory details, we are going to closed cell foam the roof to seal heat and humidity out.

The Ultra Aire can also bring in fresh air (such as it is Hot and Humid, here at SC coast). Their instructions show an 8" return in the living space, 6" fresh air return and 8" supply into the plenum after the coil.

Does anyone have experience in best way to interface (either electrically or mechanically) the HVAC & Ultra-Aire? I am concerned about backflow through elec. air cleaner if Ultra is on and HVAC is off. Also, Lennox on dehumidify is stage 1 compressor and 60% of cool setting of 1200, which is about 720 cfm (for 3 ton unit). Should both run at same time? Should Ultra Aire initiate "fan on" condition for air handler? Does back pressure from plenum affect Ultra Air flow when HVAC is on?

Outside rep's solution looks like a good route to take and essentially follows the recommendations for Thermastor's non-ducted units. We are just finishing up the construction on a new house and I took the much more complex route for the installation of a Thermasto UA-135H. It is a two story house with two separate hvac systems - one for the first floor and basement and the second for the second floor. The dehumidifier has an independent return located on the first floor and a 6" fresh air duct. The supply side of the dehumidifier is ducted to a T with one side going to the lower system and the other side to the second floor system. On the lower system, the dehumidifier supply is ducted into the supply side of the hvac system immediately downstream of the coil. The dehumidifier supply to the upstairs system is ducted into the downstream side of one of the zone dampers (master bedroom stuff). We decided that it was not worth the complexity of ducting the dehumidifier supply into each of the separate zones on the upstairs system. The lower system is not zoned.

The UA-135 is controlled by a separate digital control we located on the first floor. At this moment, only the lower hvac system has been started up - no dehumdifier yet. I can tell you that there is definitely a backflow into the dehumidifier. However, the dehumidifier did come with a backflow damper to prevent this situation, it just isn't yet working properly. I will try to let you know what other things we see happen as the various systems go through start up. Right now, the lower system is keeping the first floor stat in the lower 70's with humidity level between 45 and 50% (AS XV90 two stage variable speed furnace with Trane XL16i two stage heat pump and Carrier Thermidistat).

Your installation is somewhat similar to mine: 38,000 btus downstairs and 3 tons upstairs. AFter the roof is foamed, if the lennox units can't do the dehumidification job I will start in the attic with the Ultra-Aire and see how it does.

The downstairs unit is a downflow, with ducts in a sheetock soffit in the garage below. Not sure if it is kosher to put the supply from the dehumidifier into the side of the air handler near the floor.

How did you determine how much outside air to bring in? Or do you have it wide open?

Really looking forward to following your installation to check the results. Thanks very much for the input.

The Ultra Aire can also bring in fresh air (such as it is Hot and Humid, here at SC coast). Their instructions show an 8" return in the living space, 6" fresh air return and 8" supply into the plenum after the coil.

Does anyone have experience in best way to interface (either electrically or mechanically) the HVAC & Ultra-Aire? I am concerned about backflow through elec. air cleaner if Ultra is on and HVAC is off. Also, Lennox on dehumidify is stage 1 compressor and 60% of cool setting of 1200, which is about 720 cfm (for 3 ton unit). Should both run at same time? Both may run at the same time.

Should Ultra Aire initiate "fan on" condition for air handler? The UA is able to distribute the dry air througout the home without the a/c fan. "Fan on" wipes all the moisture off the cooling coil in 15-25 min., increasing the dehumidification load. Dried air discharged into the a/c supply flows mostly through the supply duct to the home. I am not aware of any problems with a slight air flow back through the a/c coil, fan, and air filter.
Does back pressure from plenum affect Ultra Air flow when HVAC is on? The UA is able to operate with upto .7" WG. backpressure. Most resid. a/cs are .1-.2" WG".

Thanks for the response. Wonder if it would be worthwhile to install a one way damper in the 16" supply duct. That would solve the backflow problem and probably wouldn't bother the var spd fan either. The Honeywell elec. air cleaner actually has a pre and post filter, so it seems the post filter would add somewhat of a restriction on its own.

Ultimately, I am going to run that question by the Ultra-Aire folks and Lennox for the "Official" position. I have spoken to Ultra-Aire before and their tech person was very knowledgeable, professional and knew his product... that, alone is a big plus on their side vs the competition.

Well beachwalker and others, I had hoped to have an update for you by now. But, someone decided to break into the place the other night and have a destruction fest to include the electronic controller for the dehumidifier and the thermidistat for the lower unit. Pretty sad to see. They also destroyed some of the kitchen appliances and cabinets, light fixtures, ceiling fan, etc. I haven't forgotten to keep you informed, it will just be further delayed. Besides, I promised teddy bear I'd give a full report when everything is up and running. Soon, I hope.

Here's my update:
Today they started application of 3" of closed cell foam on the roof to seal out the heat and humidity. They expect a two or three day job to complete. Here are yesterday's attic conditions at 11 AM:
air temp 96
rel humidity 65 %
dew point 82

After foam we intend to put portable dehumidifier up there in an attempt to dry out the batt insulation and duct insulation. Then we will put the Lennox units back on dehumidify setting and take more readings to see if the condensation stops or the Ultra-Aire will be necessary.